1. Field of the Invention
The present invention relates to an improved process for recovering gold from solution, and would be classified in class 75.
2. Description of the Prior Art
Many processes over the years have been developed with the express purpose of recovering gold from solution (e.g., sea water, mining tailings). The effectiveness of these processes is not questioned; however, many of these systems are dangerous, polluting, energy consuming, and allow no control of the particle size produced. Many of these processes necessitate the use of filtration and elution-complex steps, which decrease the yield and render the processes economically impractical.
U.S. Pat. No. 3,925,114 to Takahashi et al., discloses precipitating crystalline oxalates of the metals aluminum, iron, cobalt and nickel from their chloride solution to produce a magnetic alloy powder. The oxalic acid used in the process of this patent apparently does not act as a reducing agent in view of the fact that the final reducing step is performed in the presence of hydrogen (col. 3, lines 31-36). However, the use of this process in the separation of gold from solution could necessitate the formation of gold oxalate, an unnecessary step in view of the process disclosed herein, even assuming the metals aluminum, iron, cobalt and nickel to be chemical equivalents of gold for the purposes of their recovery from solution.
U.S. Pat. No. 3,736,126 discloses the recovery of gold from solution using an adsorption bed which is a polymer of acrylic or methacrylic ester. However, the process of the present invention discloses a greatly simplified method using a different adsorption bed (sodium silicate) and oxalic acid as a reducing agent, which is completely oxidized into carbon dioxide and water.
U.S. Pat. No. 3,957,505 to Homick et al., discloses precipitating gold with a reducing solution. It is, of course, well known in the art to convert ionic gold to elemental gold by use of a reducing agent.
U.S. Pat. Nos. 3,834,896 and 3,935,006 disclose recovering gold which has been adsorbed from a processing solution on activated charcoal. However, sodium silicate gel is far superior to activated charcoal as an adsorption bed, as is shown below in the example, which discloses a gold recovery of up to 99.99%. Additionally, the teaching herein is far simpler and less expensive than the methods disclosed in the two patents. Further, oxalic acid or other reducing agents are not used in the processes of these patents.
A need is therefore present for a method for recovering gold from solution which avoids the use of toxic or expensive chemicals and mitigates waste disposal and pollution control problems. Further, a need is present for a method of recovering gold from solution which allows the use of a closed-circuit, high yield, short step process allowing control of the resultant particle size.